Until this shit started. You'll see it in the big cities first. I'm sure it'll take several decades, but it will spread. The mere fact that it is even being brought up is an ominous omen of the future.
Actually I'm surprised that Boston doesn't already use AR's. I'm guessing that they were still only using/issuing shotguns, SMG's and maybe some Mini-14's during the Tsaranev incident that the BPD has now asked to be upgraded.
Only in modern day "progressive" America could you see this.